1. Field of the Invention
The present invention relates to a plasma processing apparatus, a plasma processing method, and a storage medium.
2. Description of the Related Art
Parallel plate type plasma processing apparatuses are known that have a substrate processing chamber that has therein a processing space and into which is transferred a wafer as a substrate, a lower electrode that is disposed in the substrate processing chamber and is connected to a radio frequency power source, and an upper electrode that is disposed such as face the lower electrode. In such a plasma processing apparatus, plasma is produced from a processing gas introduced into the processing space, and the wafer is subjected to plasma processing, for example etching processing, while keeping the plasma in a desired state. Moreover, such a plasma processing apparatus has an exhaust space communicated to the processing space, an exhaust pipe or the like for exhausting out residual gas and so on from the processing space is provided opening out from the exhaust space.
In such a plasma processing apparatus, apparatus components facing the processing space are covered by an insulating film made of alumite, yttria (Y2O3) or the like, but apparatus components facing the exhaust space are not covered by such an insulating film, or else are only covered by a very thin insulating film. A potential difference thus arises between the processing space and the exhaust space, and hence electrons in the plasma in the processing space are drawn into the exhaust space in accordance with the potential difference. As a result, plasma leaks into the exhaust space.
In particular, in recent years, with an aim of improving the plasma processing performance, plasma processing apparatuses in which the upper electrode is connected to a DC power source and a DC voltage is applied into the processing space have been developed. If such a DC voltage is applied into the processing space, then a large number of electrons are produced in the processing space. The large number of electrons are drawn into the exhaust space in accordance with the potential difference described above, and hence a large amount of plasma leaks into the exhaust space.
If plasma leaks into the exhaust space, then an abnormal electrical discharge may arise in the exhaust pipe, and hence the exhaust pipe may be damaged. Moreover, the plasma density in the processing space is reduced, and hence it may become difficult to carry out desired plasma processing on wafers.
Various methods have thus been developed to prevent leakage of plasma into the exhaust space. For example, it is known that leakage of plasma into the exhaust space is reduced if the anode/cathode ratio for the substrate processing chamber is increased, and hence there are known a method in which the anode/cathode ratio for the substrate processing chamber is increased, specifically a method in which the side face area of a wafer stage disposed in the substrate processing chamber is increased, a method in which an exhaust plate is provided between the processing space and the exhaust space, and a method in which the potential difference described above is eliminated through electrical connection (see, for example, Japanese Laid-open Patent Publication (Kokai) No. 2001-240973).
However, with the method in which the anode/cathode ratio for the substrate processing chamber is increased, there is a problem that the plasma processing apparatus becomes too large in size. Moreover, with the method in which an exhaust plate is provided, there is a problem that the efficiency of exhausting out residual gas and so on from the processing space is reduced. Furthermore, to eliminate the potential difference, apparatus components facing the exhaust space must be covered by an insulating film, and hence there is a problem that the manufacturing cost for the plasma processing apparatus is increased. It is thus difficult to prevent leakage of plasma into the exhaust space.